Manufacture of iron alloys



Patented Qct l, 1935 MANUFACTURE OF IRONALLOYS Ren. Perrin, Paris,France, assignor to Socit dElectrochimie dElectrometallurgie et desAcieries Electriques dUgine, Paris, France, a

corporation of France i Q 1N0 Drawing. Application February 23, 1933,

- Serial No. 658,279. In France August 29, 1932 9 Claims. (01. 75-27) fThis invention relates to improvements in the manufacture ofiron alloysof very low carbon content.

The presentpapplication is a continuation-inpart of my application,Serial No. 584,584, filed January 2, .1932, which describes thetreatment of metals with slags by violently intermixing the metal,while'in a fluid molten state, witha fluid molten slag. v

The production ofiron-alloys and in particular alloyswith chromium andmanganese, by the reducing action of carbon on the ore does not permit,even'ifthe'reducingagent is insufiicient in quantity, of obtainingverylow carbon contents. During the first phase of the refining of themetal with respect toits' carbon content by contact with theslag,'-which jat that stage of the operationis highly joxid-ized'because it is as yet insufficiently reduced,;-a considerable oxidationof the useful element such as, chromium or manganese for example takes;place and a corresponding reduction i'n =the;quality of; the alloywhich, owing to this fact; ceases;to" ':om1 )ly with the requiredcommerci'al'standards;

Reduction by metallic reducing agents such as silicon,which,maybe-a11Qyed with the basis element'of theiron alloy of;lowcarbon content to be produced, and in. all cases devoid of carbon ornearly so, permits 'of the-' working up of these low carbon alloyswithout introduction of carbon.

, It is necessaryhowever, inrthe course of this operation, to.eliminatealmost the whole of the metallic reducing a nt which tends toremain alloyed in part inth'e iron alloy to be produced, Thisoperation'which isgenerally carried out by oxidation of the reducingagent at the expense of the oxygen of a slag charged with the oxides ofthe basis elem'ents of the iron alloy which it is desired to produce,presents great difficulties.

The further the operation of eliminating the metallic reducingagent-(the silicon for example) proceeds, the more the reducible oxides of theore fused'in thepresence ofthe reducing agent are diluted byrthe oxidesto which thismetallic reducing agent has given rise and by the basesintended to neutralize it so as to disturb the chemical equilibriumwhich tends to become established. The reaction becomes sluggish, andthe exchanges between the bath of molten metal and the slag take placemore and more slowly.

Slagging out becomes necessary in order to recharge a fresh quantity ofore rich in oxide and to fuse it in order to carry on the operation ofelimination of the metallic reducing agent. slagging out operationsfollowed by a fresh charge These clog the metallic bath which is themore re fractory'the nearer it comes to the refining desired.

Now it is known that the fusion of a metallic residuum in the electricfurnace is difficult owing. 6

to the excessive conductivity of the metal. The consumption ofkilowatts'increases greatly owing to this fact and all the items of thenet cost involved in such additional consumption of energy areproportionately increased. Moreover 10 the contact of the electrode orelectrodes with the products to be. fused is prolonged thus alsoproducing a regular increase in the amount of carbon contained inproportion to the elimination of the metallic reducing agent by thereducible l5 oxides of the molten slag; Finally the prolonged heat at avery high temperature has a disastrous effect on the life of the liningsand crowns of the furnaces.

To sum up: it may be observed that in the course of the operation ofeliminating the metallic reducing agent, the fusion is rapid at thebegin ning, facilitated as it is on the one hand by the high content ofoxides in the ore to be fused (which disturbs the equilibrium in favourof a 25 rapid oxidation of the metallic reducing agent employed,accompanied by an evolution of heat brought-about by the reaction) andon the other hand by the fusible oxidized compounds formed in the courseof the reaction. The reaction then' becomes very sluggish and it becomesnecessary to slag out in order to breakup the equilibrium between themetal and the slag. The fusion of the'second charge and of thesucceeding charges if there are any, thenproceeds very slowly becausethe .bath has lost much of its fluidity by the renewing of the slag andby the reduction of .the amount of the reducing metal (silicon forexample) to about 5% or less. l I

If it is desired to obtain alloys containing a very small quantity ofthe reducing agent (0.50 or even O.l0%) ;sev,eral successive .slaggings'out will be necessary but they do not yield uniform results.

By means of the present invention these disadvantages may be avoided andin accordance therewith are obtained rapidly and with regularity ironalloys (such as ferrochromium and ferromanganese for example) with a.very, low carbon content and with the elimination as completely aspossible of the metallic reducing agent.

This invention consists substantially in bring ing about in acontinuous, rapid andintimate manner by the aid of violent intermixing,the contact of the molten metal with the oxidizing slag, the time takento eliminate the reducing 55 tact.

In all cases, whether the slag passes through the metal or the metal ispoured on to the slag, the operation lasts only about a minute and thereis no need at all to supply any external heat.

The oxidizing slag which is to act on the metal may be either previouslymelted in a suitable furnace, and be used in minimum quantity and may beof a composition strictly determined in order that the equilibrium to beattained in the course of the violent intermixing shall correspond, ineach case, to the practically total elimination of the metallic reducingagent associated with the molten alloy to be worked, or it may be runfrom the furnace itself where the alloy has been produced, into asuitable ladle, and thereupon the metal remaining in the furnace may bepoured rapidly and in a thick jet upon the slag so as to produce aviolent and turbulent intermixing of the slag and metal, as in the caseof the second example described below.

It has been found in the case'of iron alloys of 0 low carbon contentobtained according to this invention that:

(1) The elimination of the metallic reducing agent during the very shortperiod of time that the operation lasts, can be pushed as far as isdesired, that is to say until the residual content is comprised between0.20 and 0.10 which permits of responding to all the requirements ofsteel manufacturers.

(2) By working always under similar conditions (composition and quantityof the metal and of the slag in the presence thereof and also the modeof bringing them violently into intimate which this violent. intermixingof the metal and.

the slag takes place has no influence on the desired reaction, theduration of the operation being too short.

Thetem-perature of the metal is without any great influence. It issufiloient that the metal be quite fluid at the commencement of theoperation, the heat evolved in this latter permitting of retaining itsfluidity unafiected up to the end.

If it be attempted to obtain ferro chromium alloys for example by usingsilicon as the metallic reducing agent, it is possible by means of thepresent process either to obtain directly in a single operation and bythe action of an oxidizing slag melted down separately, a ferrochromiumalloy complying with current standards, that is 0.50 to 1% of Si, or todisplace the state of equilibrium in the direction of a removal of thesilicon to a greater extent by violently intermixing the slag and themetal of a charge composed of a mixture of silico-chromium, ore

desiliconized (Si comprised between 0.50 and 1%) by the first violentintermixing operation is again violently intermixed with a slag whichhas been melted down separately and is highly oxidized. The slag whichhas thus acted on Fe-Cr with 1% of silicon as the maximum is'used againfor a first removal of silicon from a new heat of silicochromium byviolent intermixing. Said slag is in the meanwhile kept liquid in thefurnace for the preparation of oxidizing slag for desiliconizing.

The quantity of slag to be used will be merely a function of the amountof silicon contained in the ferro-silicon-chromium alloy from which thesilicon is to be removed the amount of silicon contained therein beingrelated to the amount of carbon aimed at for the ferro-chromium alloywhich is to be produced.

The violent intermixing of the mass of molten metal and oxidizing slagmay be effected mechanically by a gas for example. This intermixing mustbe violent so as to limit the duration thereof.

It is possible also to carry it out in a simple and economical manner byusing a casting ladle which first receives the slag, either melted downseparately, or run from the silico chromium alloy furnace or the like.The metal is then violently run in a thick jet on to the slag preferablyfrom a considerable height and the slag finally comes to the surfacewhich multiplies the surfaces of contact between the metal and the slag.It is then found that despite the very short duration of the operationthe elimination of the metallic reducing agent (silicon for example) ,ispractically terminated as soon as the slag has collected by decantationabove the metal. The uniformity of the results obtained is perfect whenattention is paid to the conditions of the respective weights of themetal and slag and the composition thereof. With ladles of the usualdimensions the result is easily obtained.

Any means other than the ladle may also be used for carrying out theviolent intermixing operation. The ladle is however the mostadvantageous because it affords the simplest means of carrying out theoperation in order to obtain a better result. There is every advantagein burning the silicon for example solely by reducing, if .necessary,the associated oxides of the basis elements ofthe alloy rather thanfavouring the elimination thereof by having recourse to the oxygen ofthe air.

I give below by way of examples which are not limitative some operationscarried out in accordance with the present invention.

First example-The removal of the silicon from 600'kg. of metalcontaining Silicon 48.35% Iron 16.22% Chromium 35.20% Carbon 0.082%

was eifected by means of 3200 kgs. of ore (forming an oxidizing slag)melted down in a furnace constructed for this purpose, and of thefollowing composition This oxidizing slag and the metal were runsimultaneously and with violence into a ladle which, as soon as it hadreceived the constituents of the reaction, was taken to the foundryabove the ingot moulds.

About four minutes elapsed between the commencement of the run into theladle and the commencement of the casting of the metal into the ingotmoulds.

The metal of the first ingot mould had the following composition:

Silicon 0.89% Carbon 0.068%

980 kgs. of'metal of a marketable composition were obtained in a singleoperation, and a very short one compared withthat effected in a singlefurnace with the slag acting on the surface of the molten metal bathfrom which the silicon was to be removed.

Second example-300 kg. of silico-chromium of the following compositionChromium 37.20% Iron 12.30% Silicon 49.53%. Carbon 0.10%

were charged into a furnace together with 800 kg. of chromite mixed with720 kg. of lime.

In this furnace a metal of the following composition was obtainedi Cr69.80% Fe 29.05% Si 0.51% o 0.08%

The slagwas run into a ladle and when the slag had been run out of thefurnace the metal remaining in the furnace was run rapidly and in athick jet into the ladle. The metal mixed intimately with the slag witha vigorous and turbulent intermixing action.

The duration of the operation was one minute and the composition of themetal at the end-of the operation was:

Cr 70.50% c-.- -r 0.07% Si 0.08% Fe -r A 28.90%

In a few seconds therefore the removal of the silicon had been pushedvery much further, owing to the intimate contact producedthroughoutbetween the metal from which the silicon was to be removedandthe still oxidized slag, which was in contact in the furnace beforeevacuation into the ladle. This result could only have been obtainedformerly with a complementary slagging out and a refining of about anhour without any certitude of obtaining the removal of the silicon tosuch a degree.

What I claim is: v v e 1. A process for manufacturing from an. ironalloy containing a substantial amount of a reducing agent and having avery low carbon content, an alloy practically free of reducing agent,which consists in violently intermixing said alloy in a molten conditionwith a very fluid previously molten slag capable of oxidizing thereducing agent present in the alloy, the violence being such as to forman intimate mixture in a short period of time of the slag and the alloy,and separating the slag from the alloy freed of reducing agent.

2. A process for manufacturing from an iron alloy containing asubstantial amount of silicon and very little carbon, an alloypractically free of silicon, which consists in violently intermixingalloy in a molten state, which consists in violently intermixing withthe said iron alloy a very fluid previously molten oxidizing slag, theviolence being such that in the short period of time required to oxidizethe said reducing agent an intimate mixture of slag and alloy iseffected, and separating the slag containing the oxidized reducing agentfrom'the' iron alloy.

4. A process for collecting in a slag in an oxidized condition a highpercentage of a reducing agent present in an iron alloy, which consistsin violently intermixing with said iron alloy in a molten condition aslag capable of oxidizing the said reducing agent and of dissolving thereducing agent oxide so formed, and separating the ironalloy.

5. A-process for manufacturing an iron alloy practically freed ofreducing agent and having a very low content of carbon which consists inimparting to a. mass of a molten iron alloy-containing a very lowpercentage of carbon and a high percentage of a reducing agent, acertain amount of kinetic energy and utilizing said energy for forciblybringing together said iron alloy and a mass of very fluid moltenoxidizing slag so as to atomize and violently intermix said slag withthe iron alloyfor such a period of time as to oxidize nearlyinstantaneously substantially the whole of the said reducing agent, andthen separating the slag from the metal. v

6. A process for manufacturing an iron alloy very poor in reducing agentand having a very' low content of carbon, which consists in causing amass of very fluid previously molten oxidizing slag to be violentlyintermixed in a state of fine division and for a short period of time,with a mass of molten iron alloy containing a reducing agent insubstantial proportion, said finely divided slagito rise in and throughthe said iron alloy and to collect on the surface thereof.

7. A process for manufacturing an iron alloy very poor in reducing agentand having a very low content of carbon, which consists in treating in afurnace a raw iron alloy containing verylittle carbon and a highpercentage of reducing agent by means of a very fluid oxidizing slag forsuch a period of time as to lower sensibly the content of reducing agentin the iron alloy and then violently intermixing the said slag andthesaid iron alloy for such a short period of time and with such aviolence as to lower to a very small percentage the content of reducingagent of the iron alloy, and then separating the slag from the ironalloy.

8. A process for manufacturing an iron alloy having a very small contentof reducing agent when starting from a massof raw iron alloy having ahigh content of reducing agent, which consists in placing at the bottomof a ladle a mass of previously molten very fluid ,oxidizing slag andrapidly pouring the said mass of raw iron alloy in thick jet onto thesaid mass of slag with such violence as to cause a rapid intermixing totake place between the mass of alloy and the mass of and allowing thetooxidize and to remove from the 'iron alloy into the slag the greaterpart of the reducing agent, and then separating the slag from the ironalloy.

9. A process for manufacturing an iron alloy having a very low contentof reducing agent by starting from a mass of raw iron alloy having ahigh content of reducing agent, which consists in placing at the bottomof a. ladle a mass of a previously molten very fluid oxidizing slag andpouring the said mass of raw iron alloy in thick jet and from aconsiderable height onto the said mass of slag, and then separating theslag from the iron alloy.

RENE PERRIN.

